Use of an EM simulator appears
to be in order to get a meaningful field pattern
and input impedance. My cheap FM stereo antenna
works great when I bend it in the middle (approximately)
to get the best pickup in my somewhat rural location.
A couple free EM programs are available on the
"Antenna, Electromagnetics & Transmission Line
Simulators" area on the software page.
Let us know what you come up with.
- Kirt Blattenberger